To elucidate the functions of amino acid polymorphisms at codons 883 and 905 in the G subunit of Protein Phosphatase 1 (PP1), stably transfected mouse muscle cell C2C12 clones were selected for expression of the different protein variants. Unfortunately, the level of protein expression appeared to be regulated by the extent of cell differentiation, which was difficult to synchronize among the clones. In collaboration with Dr. Barbara Kahn?s lab, recombinant adenovirus vectors expressing the different protein variants were constructed. Recombinant adenoviruses that express the most protein of each type were propagated and purified to infect rat muscle cell L6 myotubes. A preliminary glycogen synthesis assay on L6 myotubes infected with adenovirus expressing wild type G subunit showed an increase of basal and insulin-stimulated levels as compared to control infected cells. Further study on the effects of overexpressed G subunit variants on glycogen synthesis and glycogen synthase activity in L6 myotubes will be pursued.